Plasma processing has long been employed for processing substrates (e.g., wafers or flat panels) into electronic products (e.g., integrated circuits or display panels). In plasma processing, one or more gases may be energized and transformed into plasma for processing (e.g., depositing, cleaning, or etching) a substrate.
To maximize substrate processing throughput, to save space, and to maximize efficiency, cluster tools have been employed to process a plurality of substrates in parallel. In a cluster tool approach, multiple plasma processing chambers may be coupled together into a cluster plasma processing system. These chambers may share certain common resources such as certain data processing capabilities, loading robot arms, wafer storage cassettes, exhaust ducting, etc. The plurality of substrates may be processed using the same recipe or using different recipes at the same time in a cluster tool.
Since each chamber may require, depending on the recipe employed, a combination of gases, multiple gas feeds are typically provided to each chamber. Each of the gas feeds may supply a specific gas (such as N2, O2, CHF3, C4F8, etc.). A mass flow controller (MFC) associated with each gas feed at each chamber meters the amount of gas flow required (e.g., a given cubic foot per minute of N2) for a required amount of time to satisfy the recipe requirement. Since a separate MFC is required for each gas feed, a chamber may have multiple MFCs to handle the different types of gas that may be called for by the recipe.
In the past, each chamber receives and regulates its own gas feed supply in order to keep the MFC performance within specification. Regulating the gas fed such that the input pressure to the MFC remains relatively stable is important for accurate MFC performance, even for MFC that are advertised to be pressure insensitive. Due to cost and spatial constraints, the trend has been to share a regulator among multiple MFCs if these MFCs all supply the same type of gas (such as N2). This approach, known by some as the “single line drop” approach, involves using a shared manifold (essentially a branching network of conduits) to supply a given gas (such as N2) from one regulator to multiple MFCs. FIG. 1 shows such a single line drop approach wherein regulator 102 is employed to regulate the input pressure for MFC 104, MFC 106, and MFC 108, the input ports of all of which are connected to shared regulator 102 via shared manifold 110. Although not shown in FIG. 1, the outputs of the MFCs are coupled to supply a gas to different processing chambers.
One advantage of the single-line-drop approach is lower acquisition and maintenance costs and reduced complexity since only one regulator needs to be purchased, calibrated, certified, maintained, serviced, and/or monitored for a plurality of MFCs. Another advantage of the single-line-drop approach is spatial efficiency, since space utilization in the vicinity of each chamber is often at a premium. By reducing the number of regulators (and oftentimes, the associated gauges and other associated components and tubings) in the vicinity of the chamber, more room can be spared for other required components (such as control electronics, heaters, various electro-mechanical components, etc.) which may be needed proximal to the chamber. This is particularly true if the regulator can be positioned remotely from the MFCs such that the regulator does not need to be positioned near the chamber(s).
However, it has been found that when multiple MFCs share a single regulator, processing performance suffers in many cases. For example, it has been found that etch profile and/or uniformity and/or yield has been affected in some cases. Embodiments of the invention seek to improve the processing performance for cluster tools using the single-line-drop approach.